When polyvinyl chloride, antimony trioxide, and zinc oxide are added to a low density flexible and semiflexible polyetherurethane flame retardant foam formulation including the usual tertiary amines, water, and metal containing catalyst and the formulation is run on production equipment as commercially used to form buns (loaves or slabs) having, for example, a cross-section of about 30 .times. 76 inches and a length of about 40 feet or more, the foam discolors (dark pink or purple) in the center section of the bun as to be virtually unsalable as is commercially.
The only external heat applied to the bun as it moves down the conveyor is that received when it passes through an oven at a speed of about 5 to 12 feet/min. and at a temperature of about 180.degree. F. for the purpose of reducing or eliminating surface tack so that the outside paper can readily be removed without tearing large chunks from the foam.
At the end of the conveyer the buns are removed and stored for about 24 hours without any external heat being applied to permit the foam to finally cure or stabilize by itself. Then the foam is slit into mattress size units or into other sizes for further manufacturing operations. Even at this time the temperature of the center of the bun is well above room temperature.
The exothermic heat of reaction of the foam forming ingredients during foaming reaches temperatures of from about 270.degree. to 350.degree. F. These temperatures are determined by a pyrometer probe at the end of the conveyor line and can be higher than shown considering that the mass of the pyrometer is greater than that of the surrounding foam.
Accordingly, it is a primary object of this invention to avoid the difficulties alluded to above, and to provide flexible and semiflexible polyetherurethane flame retardant low density foams containing halogen containing polymers, antimony trioxide, and zinc oxide and which exhibit resistance to or freedom from discoloration after foaming and to provide a method for making the same.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and example.